HOUSTON -- Investigators are baffled by the fatal shootings last week of a Chinese-American family of four, including two young boys, at their suburban Houston home.

Authorities have not yet determined a motive for the slayings nor identified any suspects, Harris County Sheriff Adrian Garcia said Tuesday. All four victims, including the boys aged 7 and 9, were shot in the head.

The names of the victims have not been released as authorities tried to contact relatives of the family. Authorities said the husband and wife were naturalized U.S. citizens who had emigrated from China. They did not say when the family arrived in the United States.

Garcia said deputies went to the family's Cypress home last Thursday after the husband's co-workers became concerned when he hadn't shown up for work for several days. Deputies found the back door open and inside discovered a "horrific crime scene," Garcia said.

Harris County Sheriff's Office Sgt. Felipe Rivera said the victims were found in their bedrooms. He declined to give other details of the crime scene, only saying they had not been tied up and that no weapons were found at the home.

"We have no other information that will speak to a motive, as to why this occurred," Garcia said. "From all indications, they were a quiet family, they were the average family. ... I am bothered by the loss of life of two children."

Autopsies done by the Harris County Institute of Forensic Sciences have ruled the deaths as homicide. Garcia said authorities don't know the type of weapon used in the killings.

Rivera said investigators found signs of forced entry via a window but that it was unclear if it was recent damage. Investigators don't know if anything was taken from the home.

"It is baffling," Rivera said of the case.

The family's father -- a mechanical engineer for Cameron, a Houston-based oil and gas industry equipment manufacturer -- last worked Jan. 24. Cameron spokeswoman Sharon Sloan confirmed the man had worked for the company but declined to comment further.